Software Upgrade for BBC HD on Freeview HD
R&D do much of the development for the television distribution systems of the BBC. For the BBC HD service as carried on Freeview HD there have been some recent changes- Phil Layton explains:
The Freeview HD platform has always been specified to provide a 1080p25 capability. This is why STBs are mandated to have a 1080p50 output to enable seamless up-conversion to a mode which is guaranteed to be present in all display devices. A great deal of material is shot natively at 1080p25 and there are significant advantages in maintaining 1080p25 through to the viewer's display. Within a single programme interlaced may be used for moving credits, cross-fades and studio shots whereas progressive may be used for location shot material.
Up until now this capability has not been exploited and 1080p25 material was encoded using a 1080i25 encoding mode. But after a software upgrade on the 22nd/23rd March the HD encoder supporting BBC HD on Freeview HD has been set-up to automatically detect progressive material and change
encoding mode appropriately. The encoded bitstream can only change at each GOP boundary to ensure decoders maintain a consistent display. This means that each coded video sequence either contains interlaced or progressive pic_struct values within the bitstream. The transitions between interlaced and progressive modes are entirely dependent upon how a programme has been made.